title: Regulation of endoplasmic reticulum Ca(2+) oscillations in mammalian eggs.
abstract: Changes in the intracellular concentration of free calcium ([Ca(2+)]i) regulate diverse cellular processes including fertilization. In mammalian eggs, the [Ca(2+)]i changes induced by the sperm unfold in a pattern of periodical rises, also known as [Ca(2+)]i oscillations. The source of Ca(2+) during oscillations is the endoplasmic reticulum ([Ca(2+)]ER), but it is presently unknown how [Ca(2+)]ER is regulated. Here, we show using mouse eggs that [Ca(2+)]i oscillations induced by a variety of agonists, including PLCζ, SrCl2 and thimerosal, provoke simultaneous but opposite changes in [Ca(2+)]ER and cause differential effects on the refilling and overall load of [Ca(2+)]ER. We also found that Ca(2+) influx is required to refill [Ca(2+)]ER, because the loss of [Ca(2+)]ER was accelerated in medium devoid of Ca(2+). Pharmacological inactivation of the function of the mitochondria and of the Ca(2+)-ATPase pumps PMCA and SERCA altered the pattern of oscillations and abruptly reduced [Ca(2+)]ER, especially after inactivation of mitochondria and SERCA functions. We also examined the expression of SERCA2b protein and found that it was expressed throughout oocyte maturation and attained a conspicuous cortical cluster organization in mature eggs. We show that its overexpression reduces the duration of inositol-1,4,5-trisphosphate-induced [Ca(2+)]i rises, promotes initiation of oscillations and enhances refilling of [Ca(2+)]ER. Collectively, our results provide novel insights on the regulation of [Ca(2+)]ER oscillations, which underlie the unique Ca(2+)-signalling system that activates the developmental program in mammalian eggs.
authors.affiliation: Department of Veterinary and Animal Sciences, University of Massachusetts Amherst, 661 North Pleasant Street, Amherst, MA 01003, USA.
authors.forename: Takuya
authors.initials: T
authors.lastname: Wakai
authors.forename: Nan
authors.initials: N
authors.lastname: Zhang
authors.forename: Peter
authors.initials: P
authors.lastname: Vangheluwe
authors.forename: Rafael A
authors.initials: RA
authors.lastname: Fissore
mesh_terms: D000818:Animals; D061207:Calcium Ionophores / Q000494:pharmacology; D020013:Calcium Signaling; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D054801:Phosphoinositide Phospholipase C / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D013849:Thimerosal / Q000494:pharmacology
chemical_list: D061207:Calcium Ionophores; D013849:Thimerosal; D015759:Ionomycin; D054801:Phosphoinositide Phospholipase C; C499234:Plcz1 protein, mouse; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C506947:Atp2a2 protein, mouse
keywords: Ca2+ oscillations; Egg activation; Endoplasmic reticulum; Fertilization; Oocyte maturation; SERCA